1. Field of the Invention
The present invention relates to a resist composition, and more specifically it relates to a chemical amplification resist composition that can be developed by a basic aqueous solution after exposure. The invention further relates to a negative resist pattern forming method employing the resist composition. The resist composition of the-invention can be used to form intricate negative resist patterns that have practical sensitivity without swelling. Furthermore, the present invention relates to electronic devices including semiconductor devices such as LSI and VLSI and magnetic recording heads such as MR heads, and the production process thereof.
2. Description of the Related Art
Higher integration of semiconductor integrated circuits has progressed to the current situation in which LSIs and VLSIs are feasible, and the minimal wiring widths of wiring patterns have reached the range of 0.2 Am and smaller. This has rendered essential the establishment of microworking techniques, and in the field of lithography the demand has largely been met by shifting the ultraviolet wavelengths of light exposure sources to shorter wavelengths in the far ultraviolet range; it has been predicted that light exposure techniques employing light sources with wavelengths in the deep ultraviolet range will soon be implemented in mass production processes. At the same time, development has been rapidly progressing with resist materials that exhibit lower light absorption of the aforementioned shorter wavelengths, have satisfactory sensitivity and also exhibit high dry etching resistance.
In recent years much research has been conducted in the field of photolithography employing as the exposure light sources krypton fluoride excimer lasers (wavelength: 248 nm, here under abbreviated to KrF), as a new light exposure technique for manufacture of semiconductor devices, and they are being widely used for mass production. H. Ito et al. of IBM, U.S.A. have already developed resist compositions based on the concept of xe2x80x9cchemical amplificationxe2x80x9d, as resists with high sensitivity and high resolution that are suitable for such short wavelength light exposure. (See, for example, J. M. J. Frechet et al., Proc. Microcircuit Eng., 260(1982), H. Ito et al., Digest of Technical Papers of 1982 Symposium on VLSI Technology, 86(1983), H. Ito et al., xe2x80x9cPolymers in Electronicsxe2x80x9d, ACS Symposium Series 242, T. Davidson ed., ACS, 11(1984), and U.S. Pat. No. 4,491,628). As is readily understood from these publications, the fundamental concept of chemical amplification resist compositions is based on higher sensitivity through an improved apparent quantum yield achieved by a catalytic reaction in the resist film.
There may be cited the very widely used and researched chemical amplification resist type that comprises t-butoxycarbonyl polyvinylphenol (t-BOCPVP) and further contains a Photo Acid Generator (PAG), which has the function of generating an acid upon light exposure; xe2x80x9cpost exposure bakingxe2x80x9d (PEB) of the exposed sections of the resist results in loss of the t-BOC groups to give isobutene and carbon dioxide. The proton acid produced upon loss of t-BOC serves as a catalyst promoting a deprotection chain reaction, which greatly alters the polarity of the exposed sections. With this type of resist, an appropriate developer can be selected to match the large change in polarity of the exposed sections, to easily form an intricate resist pattern with no swelling.
Incidentally, one of the high-resolution techniques widely used in recent years is a method employing a mask that alters the phase of light, known as a phase-shift mask or Levenson mask, and it holds promise as a method that can give resolution below the exposure light wavelength and an adequate focal depth. When such masks are used, negative resists are usually appropriate due to restrictions of the mask pattern, and this has created a strong demand for provision of negative resists. When KrF is used as the light source, these masks are considered for applications in which resolution of under 0.20 xcexcm is required, and this has led to spurring development of high performance resists that can resolve intricate patterns without swelling, as mentioned above. There has also been abundant research in the field of lithography using argon fluoride excimer lasers (wavelength: 193 nm, hereunder abbreviated to ArF) and electron beam (EB) sources, with even shorter wavelengths than KrF, and it is an essential technique for formation of patterns of less than 0.13 xcexcm. The development of a negative resist that can be used for ArF, EB and the like on which more advanced microworking depends, will therefore provide many industrial advantages.
Alkali-developable negative resists for KrF and EB include those based on polar reaction caused by an acid-catalyzed reaction [for example, H. Ito et al., Proc. SPIE, 1466, 408(1991), S. Uchino et al., J. Photopolym. Sci. Technol., 11(4), 553-564(1998), etc.] and those based on acid catalyzed crosslinking reaction [for example, J. W. Thackeray et al., Proc. SPIE, 1086, 34(1989), M. T. Allen et al., J. Photopolym. Sci. Technol., 7, 4(3), 379-387(1991), Liu H. I., J. Vac. Sci. Technol., B6, 379(1988), etc.]. Crosslinkable types of negative resists for ArF are also known [for example, A. Katsuyama et al., Abstracted Papers of Third International Symposium on 193 nm Lithography, 51(1997), K. Maeda et al., J. Photopolym. Sci. Technol., 11(4), 507-512(1998), etc.]
However, despite the strong demand for a high performance negative resist that can be used for high resolution techniques employing the aforementioned phase-shift masks or Levenson masks and that can be applied for KrF, ArF and EB, the existing negative resists that are practical for use consist of only the crosslinkable types mentioned above. Crosslinkable negative resists accomplish patterning by utilizing a crosslinking reaction to increase the molecular weight at the exposed sections, thus producing a difference in solubility in the developing solution with respect to the unexposed sections; it is therefore difficult to increase contrast, and unlike resists based on polar reaction caused by an acid-catalyzed reaction, it is impossible to circumvent the limitations on microworking due to pattern swelling.
As described above, when negative chemical amplification resists are examined, they are found to be largely classified as types that contain in the resist an alkali-soluble base resin, a photoacid generator that decomposes upon absorption of image-forming radiation to release an acid and a substance that causes a polarity change due to the acid-catalyzed reaction, and types that contain in the resin an alkali-soluble base resin, a photoacid generator that decomposes upon absorption of image-forming radiation to release an acid and a substance that can cause crosslinking reaction within the resin. The former chemical amplification resists that utilize a polar reaction typically make use of a pinacol transfer reaction as disclosed, for example, in R. Sooriyakumaran et al., SPIE, 1466, 419(1991) and S. Uchino et al., SPIE, 1466, 429(1991). The acid-catalyzed reaction in such a resist proceeds in the following manner. 
That is, the alkali-soluble pinacol is affected by the acid and heat, being rendered alkali-insoluble. However, such chemical amplification resists have a problem in terms of resolution. Although the pinacol itself is rendered alkali-insoluble by the acid-catalyzed reaction as explained above, the alkali-soluble base resin itself does not react and it is therefore impossible to achieve a sufficient dissolution rate difference.
Chemical amplification resists are also disclosed in Japanese Unexamined Patent Publications (Kokai) Nos. 4-165359, 7-104473, 11-133606, and elsewhere. For example, Japanese Unexamined Patent Publication (Kokai) No. 4-165359 discloses a radiation-sensitive composition characterized by containing an alkali-soluble polymer compound, a secondary or tertiary alcohol with a hydroxyl group on a carbon directly bonded to an aromatic ring, and an acid precursor that generates an acid upon radiation exposure. The secondary or tertiary alcohol used here may be, for example, a phenylmethanol derivative represented by the following formula. 
where A represents an alkyl or methylol group of no more than 4 carbons. 
where R4 and R5 may be the same or different, and each represents a hydrogen atom or a phenyl group. The acid-catalyzed reaction in the resist proceeds in the following fashion. 
As mentioned above, the alkali-soluble polymer compound is affected by the acid and heat so that the secondary or tertiary alcohol forms a dehydration bond, thus becoming alkali-insoluble. However, because an aromatic ring is included in the secondary or tertiary alcohol that contributes to the acid-catalyzed reaction, although its presence in the chemical amplification resist is believed to be for improved etching resistance, this raises the problem of restrictions on the exposure light source. This is because the aromatic ring has high light absorption and is therefore particularly unsuitable for application to short wavelength KrF lasers and ArF lasers (argon fluoride excimer laser: wavelength: 193 nm). The other purpose of the aromatic ring is thought to be conjugated stabilization of the double bond produced by dehydration, but the hydroxyl group is bonded to the carbon directly bonded to the aromatic ring. With this structure, the dehydration in the alcohol molecule constitutes the primary reaction whereas reaction does not occur with the polar groups (phenolic hydroxyl group, etc.) of the base resin, such that the intended polar change is reduced. Furthermore, since no double bond is produced by dehydration with a primary alcohol, the use is limited to a secondary or tertiary alcohol, and it is desirable to eliminate this restriction in order to allow a wider scope of application.
Chemical amplification resists utilizing the latter acid-catalyzed crosslinking reaction typically make use of crosslinking reaction of an alkali-soluble resin with a melamine-based crosslinking agent such as methoxymethylol melamine, and such are disclosed, for example, in M. T. Allen et al., J. Photopolym. Sci. Technol., 7, 4(3), 379-387(1991). The crosslinking reaction in the resist proceeds in the following fashion. 
The use of a melamine-based crosslinking agent such as in this type of chemical amplification resist can provide an effect of lower alkali solubility through gelling reaction of the base resin (increased molecular weight by crosslinking of the resin) and through depolarization of the resin polar groups (phenolic hydroxyl groups) as a result of the crosslinking. However, the methoxymethylol melamine used here as the crosslinking agent inherently has low polarity, and therefore a sufficient dissolution rate difference cannot be produced. It is desirable to provide a resist that has high polarity of the resin and additives prior to light exposure, and low polarity of the resin and additives after light exposure.
The present invention is directed to overcome the aforementioned prior art problems.
In one aspect thereof, the present invention is directed to provide a novel resist composition that allows the use of basic aqueous solutions (standard alkali developers) as the developers, that have practical sensitivity and that can form intricate negative resist patterns with no swelling.
It is another object of the invention to provide a novel resist composition that is suitable for deep ultraviolet image-forming radiation, typical of which are KrF and ArF excimer lasers, as well as electron beams, and that also has excellent dry etching resistance.
It is yet another object of the invention to provide a novel resist composition that gives a high polarity difference between the exposed sections and unexposed sections, to form intricate patterns with high sensitivity, high contrast and high resolution.
It is still another object of the invention to provide a resist pattern forming method that employs the novel resist composition.
In another aspect, it is an object of the present invention to overcome the aforementioned problems associated with the prior art techniques by providing a resist composition that has a large dissolution rate difference between the exposed sections and unexposed sections, to allow formation of intricate patterns with high sensitivity, high contrast and high resolution.
It is another object of the invention to provide a resist composition that allows the use of basic aqueous solutions (standard alkali developers) as the developers.
It is yet another object of the invention to provide a resist composition that is suitable for deep ultraviolet image-forming radiation, typical of which are KrF and ArF excimer lasers, as well as electron beams, and that also has excellent dry etching resistance.
It is still yet another object of the invention to provide a resist pattern forming method employing a resist composition according to the invention.
In still another aspect, one object of the present invention is to provide a novel negative resist composition free of the problem of pattern swelling and capable of forming a fine pattern with practically usable sensitivity using a short wavelength light source for exposure. The object of the present invention includes providing a novel resist composition capable of coping with an exposure light source in the deep ultraviolet region, represented by KrF or ArF excimer laser, and having excellent dry etching resistance. The object of the present invention further includes providing a novel resist composition capable of greatly differentiating the polarity between the exposed area and the unexposed area and thereby forming a fine pattern favored with all of high sensitivity, high contrast and high resolution.
Another object of the present invention is to provide a method for forming a resist pattern using the above-described resist composition.
In addition to the above problems, there is another problem to be solved by the present invention.
The present inventors have already proposed in Japanese Patent Application No. 11-260815 a novel polarity-changing, high-performance negative resist composition as a resist that can meet the demands described above. The proposed resist composition employs an alicyclic alcohol, and preferably a tertiary alcohol with a stereochemically fixed structure, as the alkali-insolubilizing additive. The resist composition can form an intricate negative resist pattern with a larger polarity difference between the exposed and unexposed sections and higher sensitivity, contrast and resolution compared to conventional resists, by the reaction shown in formula (13) below, for example. 
As a result of more diligent research on the aforementioned negative resists, the present inventors have completed the present invention upon determining the most suitable conditions for obtaining resist patterns with high sensitivity and high resolution.
That is, the present invention has been completed upon finding that it is possible to provide a negative resist composition with even higher-sensitivity and higher resolution by setting numerical limits on the molecular weight distribution of the base resin used according to the first aspect of the invention, and by limiting the range for the molecular weight of the base resin used according to the second aspect.
It is therefore one object of the invention to provide a novel negative resist composition with vastly improved sensitivity and resolution.
It is another object to provide a negative resist pattern forming method employing the novel negative resist composition.
Further, the present invention has an object to provide a process for the production of electronic devices using novel negative resist composition of the present invention, and electronic devices produced upon application of such production process.
The above objects and other objects of the present invention will be appreciated from the following descriptions of the present invention referring to preferred embodiments thereof.
First Invention:
As a result of diligent research aimed at achieving the objects in the first aspect of the present invention, the present inventors have completed the present invention upon discovering that for chemical amplification resist compositions, it is important to use as the base resin a film-forming polymer which has an alkali-soluble group in the molecule and is soluble in basic aqueous solutions, and to include in the polymer a monomer unit with an alcohol structure, preferably a tertiary alcohol structure, on the side chain. When the photo acid generator used in combination with the film-forming polymer in the resist composition of the invention absorbs image-forming radiation and decomposes, it produces an acid which either induces reaction between the alcohol structure on the side chain of the monomer unit in the polymer and the portion of the same polymer with the alkali soluble group, or else protects the alkali-soluble group. As a result, the exposed sections that have absorbed the image-forming radiation are rendered alkali-insoluble, allowing formation of a negative resist pattern.
The present invention (first invention) resides in a negative resist composition which is developable in basic solutions, characterized by comprising
(1) a film-forming polymer which is itself soluble in basic aqueous solutions, and contains a first monomer unit with an alkali-soluble group and a second monomer unit with an alcohol structure capable of reacting with the alkali-soluble group, and
(2) a photo acid generator which, when decomposed by absorption of image-forming radiation, is capable of generating an acid that can induce reaction between the alcohol structure of the second monomer unit and the alkali-soluble group of the first monomer unit, or protect the alkali-soluble group of the first monomer unit, and by being itself soluble in basic aqueous solutions, but upon exposure to the image-forming radiation being rendered insoluble in basic aqueous solutions at its exposed sections as a result of the action of the photo acid generator.
In another aspect of the present invention, the present invention resides in a negative resist pattern forming method, characterized by comprising the following steps:
coating a negative resist composition of the invention onto a target substrate,
selectively exposing the formed resist film to image-forming radiation that can induce decomposition of the photo acid generator of the resist composition, and
developing the exposed resist film with a basic aqueous solution.
Second Invention:
As a result of diligent research aimed at achieving the objects in the second aspect of the present invention, the present inventors have completed the present invention upon discovering that for chemical amplification resist compositions, it is effective to include, in addition to a base resin composed of an alkali-soluble polymer and a photoacid generator capable of decomposing upon absorption of image-forming radiation to generate an acid, also an alicyclic alcohol, and especially a tertiary alcohol with a stereochemically fixed structure, as an additive that can render the resist alkali-insoluble.
The present invention (second invention) therefore provides a negative resist composition characterized by comprising a combination of the following reaction components:
(1) a base resin composed of an alkali-soluble polymer,
(2) a photoacid generator capable of decomposing upon absorption of image-forming radiation to generate an acid, and
(3) an alicyclic alcohol with a reactive site that can undergo dehydration bonding reaction with the polymer of the base resin in the presence of the acid generated by the photoacid generator.
The present invention also provides a negative resist pattern forming method, characterized by comprising the following steps:
coating a negative resist composition according to the invention onto a target substrate,
selectively exposing the formed resist film to image-forming radiation that can induce decomposition of the photoacid generator of said resist composition, and
developing said resist film with a basic aqueous solution after post exposure baking.
The resist composition of the invention encompasses, as a preferred mode in addition to the description in the claims, a negative resist composition characterized in that the base resin is a phenol-based polymer, a (meth)acrylate-based polymer or a mixture thereof.
Third Invention:
As a result of extensive investigations to solve the above-described problems in the third aspect of the present invention, the present inventors have found that for the chemically amplified resist composition, the matter of importance is to use a film-forming first polymer having an alkali-soluble group and being soluble in a basic aqueous solution as the base resin and at the same time to contain a second polymer having an alcohol structure on the side chain in the resist composition. The present invention has been accomplished based on this finding.
More specifically, the above-described object of the present invention can be attained, by a negative resist composition comprising a first polymer having an alkali-soluble group, a second polymer having on the side chain an alcohol structure capable of reacting with the alkali-soluble group, and a photoacid generator capable of generating an acid which decomposes by absorbing a radiation for forming an image and excites a reaction between the alkali-soluble group of the first polymer and the alcohol of the second polymer, wherein the composition itself is soluble in a basic aqueous solution and upon exposure to the radiation for forming an image, the exposed area becomes insoluble in the basic aqueous solution under the action of the photoacid generator.
According to the present invention, when the negative resist composition is exposed to a radiation for forming an image, the photoacid generator generates an acid capable of exciting an reaction between the alkali-soluble group of the first polymer and the alcohol of the second polymer, as a result, an acid catalytic reaction takes place, whereby the exposed area can be insolubilized in a basic aqueous solution.
Furthermore, in the negative resist composition of the present invention, the reaction excited by the photoacid generator can be a protection-type reaction of protecting the alkali-soluble group and/or an insolubility promotion-type reaction of promoting the insolubilization of the alkali-soluble group in a basic aqueous solution.
Upon reaction of the alcohol with the alkali-soluble group of the first polymer, the reaction site of the alcohol forms an ether bond, an ester bond or the like to protect the alkali-soluble group of the first polymer and thereby insolubilize the alkali-soluble group in a basic aqueous solution. As a result, a great difference arises in the polarity between the unexposed area and the exposed area. By virtue of this, the negative resist composition can be free of the problem that the exposed area swells, and favored with all of high sensitivity, high contrast and high resolution.
Accompanying the above-described protection-type reaction, an alkali insolubility promotion-type reaction of diminishing the property of the alkali-soluble group in the first polymer may be allowed to proceed. In this case, the difference in the solubility from the unexposed area increases, therefore, a negative fine resist pattern can be similarly formed.
Furthermore, in the negative resist composition of the present invention, the alcohol structure is preferably a tertiary alcohol structure. When the second polymer contains a tertiary alcohol structure on the side chain, a dehydration reaction readily takes place with the alkali-soluble group of the first polymer and the reaction between the first polymer and the second polymer can be accelerated.
In addition, in the negative resist composition of the present invention, the tertiary alcohol structure may be a structure represented by any one of the following formulae (1) to (4): 
wherein R represents an atomic group connected to the main chain of the second polymer and R1 and R2 each is an arbitrary alkyl group having from 1 to 8 carbon atoms containing a linear or branched structure or a cyclic structure; 
wherein R has the same meaning as defined above, n is a number of 2 to 9 and Rx is a group having from 1 to 8 carbon atoms containing a linear or branched structure or a cyclic structure; 
wherein R has the same meaning as defined above, Y represents hydrogen atom or an arbitrary alkyl group having from 1 to 6 carbon atoms, an alkoxycarbonyl group, a ketone group, a hydroxyl group or a cyano group; 
wherein R and Y each has the same meaning as defined above.
The tertiary alcohol having the structure shown above can undertake the reaction of insolubilizing the alkali-soluble group of the first polymer in the presence of an acid generated from the photoacid generator and thereby more surely insolubilize the exposed area in a basic aqueous solution.
It is sufficient if the second polymer has compatibility with the first polymer, and the first polymer and the second polymer each is not particularly limited on the main chain moiety thereof. However, in the negative resist composition of the present invention, the first polymer and the second polymer each may comprise at least one monomer unit selected from the group consisting of acrylic acid-type, methacrylic acid-type, itaconic acid-type, vinylbenzoic acid-type, vinylphenol-type, bicyclo[2.2.1]hept-5-ene-2-carboxylic acid-type and N-substituted maleimide-type compounds and derivatives thereof. The monomer unit of the first polymer and the monomer unit of the second polymer may be the same or different. Each polymer may be formed of a single monomer or may be in the form of a copolymer.
In the first polymer as the base resin, the ratio occupied by the monomer unit having an alkali-soluble group is not limited as long as the resin itself shows appropriate alkali solubility, however, it is necessary to take account of obtaining an appropriate alkali solubility speed which is considered practicable as the negative resist (in a 2.38% TMAH developer, a solubility speed of approximately 100 to 30,000 xc3x85/s). If such an alkali solubility speed is satisfied, a homopolymer comprising one component monomer unit may be used as the alkali-soluble base resin and this composition is preferred. Examples of such a resin include polyvinyl phenol, polyvinylbenzoic acid, polymethacrylic acid and polyacrylic acid.
In the case where the polymer comprises a monomer unit consisting of two or more components and the alkali-soluble group is a carboxyl group, the monomer unit content is preferably from 10 to 90 mol %, more preferably from 30 to 70 mol %. If the monomer unit content is less than 1 mol %, the alkali solubility is insufficient and the patterning cannot be satisfactorily performed, whereas if it exceeds 90 mol %, the alkali solubility is too strong and the dissolution in a basic aqueous solution proceeds at an excessively high speed, as a result, the patterning by the change in the polarity cannot be obtained. The monomer unit content is still more preferably from 30 to 50 mol %.
In the case where the alkali-soluble group is a phenolic hydroxyl group, the monomer unit content is preferably from 20 to 99 mol %, more preferably from 50 to 95 mol %. If the monomer unit content is less than 30 mol %, the alkali solubility is insufficient and the patterning cannot be satisfactorily performed. The monomer unit content is still more preferably from 80 to 95 mol %.
In this negative resist composition, the content of the second polymer is not particularly limited, and it may be sufficient if in view of the relationship with the first polymer, the content is large enough to maintain the alkali solubility of the composition as a whole and at the same time insolubilize the alkali-soluble group of the first polymer. In this negative resist composition, the second polymer content is preferably from 0.1 to 80 wt % based on the total polymer weight of the first and second polymers.
Furthermore, in this negative resist composition of the present invention, the molecular weight of the second polymer is not particularly limited and it may be sufficient if in view of the relationship with the first polymer, the alkali solubility of the composition as a whole can be maintained. In this negative resist composition, the molecular weight of the second polymer is preferably from 500 to 100,000.
In the negative resist composition of the present invention, a compound having an alcohol structure may further be added. In the case where the alcohol structure of the second polymer is lacking, by further adding another compound having an alcohol structure, the insolubilization of the exposed area of this negative resist in a basic aqueous solution can be accelerated without fail.
The above-described compound having an alcohol structure preferably contains a tertiary alcohol structure. This compound reacts, similarly to the second polymer having an alcohol structure, with the alkali-soluble group of the first polymer, so that the insolubilization of the alkali-soluble group of the first polymer in a basic aqueous solution can be accelerated in the exposed area.
Examples of the alcohol structure which can be used include an allyl alcohol structure and a secondary or tertiary alcohol structure. Among these, a tertiary structure is preferred. The compound having this structure is particularly effective because it can reacts with the alkali-soluble group and greatly contributes to the formation of a negative pattern.
From the standpoint that the compound having an alcohol structure must have a boiling point sufficiently high not to vaporize during the ordinary resist processing and lose its function, the boiling point of the compound having an alcohol structure is preferably at least 130xc2x0 C. or more.
In this negative resist, the compound having an alcohol structure preferably contains an alicyclic structure or a polynuclear alicyclic structure. By having such a structure, the etching resistance at the etching can also be improved.
In this negative resist composition, the compound having an alcohol structure preferably contains at least one hydroxyl group, ketone group or alkyloxycarbonyl group.
Furthermore, in this negative resist composition, the first polymer may further contain an alkali-soluble group selected from a lactone ring, an imide ring and an acid anhydride. When the first polymer contains this weak alkali-soluble group as the second monomer unit, the alkali solubility speed can be easily controlled.
In the negative resist composition of the present invention, the molecular weight of the first polymer is suitably from 2,000 to 1,000,000.
In the negative resist composition of the present invention, the photoacid generator (PAG) content depends on the strength of the acid generated after the composition is exposed to an exposure light source, however, usually, the content is suitably from 0.1 to 50 wt % (a percentage to the total polymer weight of the first and second polymers), preferably from 1 to 15 wt %. The molecular weight (weight average molecular weight) of the base resin is suitably from 2,000 to 1,000,000, preferably from 5,000 to 100,000, more preferably from 3,000 to 50,000. The molecular weight (weight average molecular weight) of the second polymer having on the side chain an alcohol structure capable of reacting an alkali-soluble group is suitably from 300 to 1,000,000, preferably from 500 to 100,000, more preferably from 1,000 to 10,000.
The resist composition of the present invention is preferably provided in the form of a solution obtained by dissolving it in a solvent selected from the group consisting of ethyl lactate, methyl amyl ketone, methyl-3-methoxypropionate, ethyl-3-ethoxypropionate, propylene glycol methyl ether acetate and a mixture thereof. The resist composition may further contain, if desired, a solvent selected from the group consisting of butyl acetate, xcex3-butyrolactone, propylene glycol methyl ether and a mixture thereof, as an auxiliary solvent.
Another object of the present invention can be achieved by a method for forming a resist pattern, comprising a series of steps for coating the negative resist composition on a treated substrate, i.e., target substrate as defined hereinafter, to form a resist film, for selectively exposing the resist film by a radiation for forming an image to accelerate the decomposition of said photoacid generator, and for developing the exposed resist film with a basic aqueous solution.
In the method for forming a resist pattern according to the present invention, the resist film formed on a treated substrate is preferably subjected to a heat treatment before and after the step of performing the selective exposure thereof. More specifically, in the present invention, the resist film is preferably subjected to a pre-baking treatment before the exposure thereof and at the same time to a post-baking treatment described above as PEB (post exposure baking) after the exposure but before the development. These heat treatments can be advantageously performed by an ordinary method.
Although the resist composition of the present invention preferably has an absorbance of 1.75/xcexcm or less at the wavelength of the exposure light source (from 150 to 300 nm) for obtaining satisfactory patterning characteristics, in the case of using EB as the light source, the absorbance is not particularly limited.
Examples of the basic aqueous solution used as the developer include an aqueous solution of a metal hydroxide belonging to Group I or II, represented by potassium hydroxide, and an aqueous solution of an organic base not containing a metal ion, such as tetraalkylammonium hydroxide. Among these, preferred is an aqueous solution of tetramethylammonium hydroxide. In order to improve the development effect, additives such as surfactant may also be added.
Fourth Invention:
The objects in the fourth aspect of the present invention are achieved by a negative resist composition wherein the molecular weight distribution of the sections rendered insoluble by light exposure is between 1 and 2 inclusive, as an invention based on limitation of the molecular weight distribution.
According to the present invention, since the insolubilized sections are formed primarily by a reaction based on polarity changes, it is possible to provide a resist composition with vastly improved sensitivity and resolution without the problem of pattern swelling.
The molecular weight distribution is the value obtained by dividing the weight average molecular weight by the number average molecular weight. With conventional resists, the molecular weight varies considerably depending on crosslinking reaction and the variation differs widely for the particular molecule; the molecular weight distribution of the insolubilized sections is therefore usually a value of from 3 to 4 or higher, whereas that of the resist composition of the invention is in the range of 1 to 2 inclusive, so that the polymer used is more uniform. Since this type of resist does not undergo xe2x80x9cgellingxe2x80x9d by molecular weight increase, it has an advantage in that the resist that has transferred the required pattern can be easily released with an organic solvent or the like.
The negative resist composition may also have the structure described in the claim, containing a base resin which comprises an alkali-soluble polymer, a photo acid generator which is capable of decomposing upon absorption of image-forming radiation to generate an acid, and an alicyclic alcohol with a reactive site that can undergo dehydration bonding reaction with the alkali-soluble group of the base resin in the presence of the acid generated by the photo acid generator.
According to the present invention, there is included an alicyclic alcohol with a reactive site that can undergo dehydration bonding reaction with the alkali-soluble group of the base resin, and therefore the polarity change is increased when it is added to an alkali-soluble polymer, while the etching resistance can also be improved. Furthermore, since the molecular weight distribution at the sections insolubilized by light exposure is in the range of 1 to 2 inclusive, it is possible to give a negative resist composition with higher sensitivity and higher resolution.
The base resin in the negative resist composition preferably has a molecular weight distribution of between 1 and 1.5 inclusive. Using a base resin with a molecular weight distribution in this range will allow the molecular weight distribution of the sections insolubilized by light exposure to be more reliably confined to the range of 1 to 2 inclusive.
Throughout this specification, a base resin with a molecular weight distribution of from 1 to 1.5 inclusive before light exposure will sometimes be referred to as a xe2x80x9cmonodisperse resinxe2x80x9d. The monodisperse resin need only be uniform to fall within the above-mentioned range, and the base resin may also have the construction of a copolymer containing a number of different monomer units.
The negative resist composition of the present invention preferably has a base resin with a weight average molecular weight of at least 2000 as described in claim 3, and more preferably the weight average molecular weight of the base resin is 3000 to 20,000. If the weight average molecular weight of the base resin is too low the sensitivity and resolution may be reduced, and if it is too high the lower solubility may result in a lower dissolution rate for the reaction, creating an undesirably low solubility. The most preferred range for the weight average molecular weight is from 5000 to 10,000. Using a base resin with a weight average molecular weight in this range can give a negative resist composition with high solubility and high resolution. Here, the preferred molecular weight is specified by the weight average molecular weight because the base resin is composed of a polymer.
From the standpoint of controlling the molecular weight of each molecule of the polymer composing the base resin used according to the second aspect of the invention, the object described above is also achieved by a negative resist composition containing a base resin which comprises an alkali-soluble polymer, a photo acid generator which is capable of decomposing upon absorption of image-forming radiation to generate an acid, and an alicyclic alcohol with a reactive site that can undergo dehydration bonding reaction with the alkali-soluble group of the base resin in the presence of the acid generated by the photo acid generator, wherein no more than 10 wt % thereof consists of components with a molecular weight of under 2000 in said base resin.
The present inventors have confirmed that using a base resin containing a low molecular weight portion with a molecular weight of under 2000 drastically reduces the sensitivity and resolution of the resist. This low molecular weight portion is believed to hamper the solubility-suppressing effect in basic aqueous solutions. It was found that when the low molecular weight components of under 2000 are limited to no more than 10 wt %, it is possible to obtain a favorable negative resist composition in which the aforementioned undesirable effect is inhibited. The low molecular weight components of below 2000 more preferably constitute no more than 3 wt % of the base resin. Here, the molecular weight is not the weight average molecular weight explained above, but rather the (actual) molecular weight of each polymer molecule composing the base resin.
By limiting the low molecular weight components with a molecular weight of below 2000 to no more than 10 wt % of the base resin it is possible to give a resist composition with high sensitivity and high resolution, but a resist composition with even higher sensitivity and resolution can be obtained by giving the base resin a monodisperse property, as mentioned above.
The base resin of a negative resist composition according to the present invention preferably contains a phenol-based compound. A phenol-based resin facilitates adjustment of the molecular weight distribution and cutting of the low molecular weight portions.
The base resin is preferably polyvinylphenol or a copolymer of vinylphenol with another monomer. Polyvinylphenol is preferred as the base resin because it is readily obtainable and its monodispersion is easy to accomplish.
The alicyclic alcohol of a negative resist composition according to the present invention preferably has an adamantane structure, as described in claim 6. An alicyclic alcohol with an adamantane structure can more readily promote insolubilization of the light exposed sections.
The alicyclic alcohol of a negative resist composition of the present invention preferably has a tertiary alcohol structure with a stereochemically fixed structure. An alcohol with such a structure can more readily promote insolubilization of the light exposed sections.
The tertiary alcohol of a negative resist composition of this invention is preferably a 1-adamantanol or a derivative thereof.
The photo acid generator of a negative resist composition according to the present invention is preferably one selected from the-group consisting of onium salts, halogenated organic substances and sulfonic acid esters.
The onium salt in the negative resist composition of this invention may be any one selected from the group consisting of the following formulas (A) to (D). 
where X=CF3SO3, CF3CF2CF2CF2SO3, SbF6, AsF6, BF4 and PF6.
The halogenated organic substance in the negative resist composition of this invention may be a triazine with a halogen in the structure or an isocyanurate with a halogen in the structure.
A high sensitivity, high resolution resist pattern may be obtained by a negative resist pattern forming method which comprises the series of steps including coating a negative resist composition according to the present invention onto a target substrate, selectively exposing the formed resist film to image-forming radiation that can induce decomposition of the photo acid generator of the resist composition, and developing the exposed resist film with a basic aqueous solution.
Furthermore, according to the present invention, there is also provided a method for the production of electronic devices using the negative resist composition of the present invention, i.e., first to fourth inventions described above.
The production process of electronic devices according to the present invention is characterized by using as a masking means a resist pattern formed from the negative resist composition of the present invention to selectively removing the underlying target substrate, thereby forming a predetermined functional element layer. The definition of the term xe2x80x9cfunctional element layerxe2x80x9d will be described hereinafter.
The production process of electronic devices is preferably carried out by the following steps:
coating the negative resist composition onto the target substrate,
selectively exposing the formed resist film to image-forming radiation that can induce decomposition of the photo acid generator of the resist composition,
developing the exposed resist film with a basic aqueous solution to form a resist pattern, and
etching the target substrate in the presence of the resist pattern as a masking means to form the functional element layer.